Cryopreservation techniques at temperatures at or below 0° C. are routinely used for long-time preservation of water-bearing or aqueous materials such as cells and tissues of plants and animals as well as foods. It is known that upon freezing these materials, ice crystals form, resulting uneven concentrations of solutes and contaminants excluded by water molecules, called ‘freeze concentration.’
To prevent freeze concentration, various compounds of low molecular weights can be added to the cryopreservation media. For example, dimethylsulfoxide (DMSO), glycerol or the like is added as a freeze-protecting agent to minimize the damages on the cells and tissues, which are otherwise caused by crystallized water in the cells on course of cryopreservation.
Thus, cells are generally suspended in a physiological solution, a culture medium which contains 5-20% cryopreservation agents such as DMSO, glycerin, ethyleneglycol and propylene glycol in a cryotube and preserved at cryogenic temperatures, −80° C. or −196° C.
Among these agents, DMSO is the most effective and frequently adopted, but it is physiologically toxic and known to cause high blood pressure, nausea and vomiting when the cells are transfused to a recipient. Further, the toxicity of DMSO tends to debilitate the cells' survival rates and/or functions after the thawed cells are cultured or transfused into a recipient's body.
Glycerin among other agents has lower cryopreservation effects and requires freezing only after keeping cell suspensions at room temperatures or non-freezing low temperatures, or accurately controlling the decreasing temperatures by the use of a program freezer or the like. Moreover, such cryopreservation agents are detrimental to the thawed cells because of their low protective effects on cell survival and functions.
In the cryopreservation of stem cells such as embryonic stem cells or iPS cells or reproductive cells such as sperms, unfertilized or fertilized eggs, a rapid freezing or vitrifaction is performed with high concentrations of cryoprotective agents such as DMSO, acetamide, propylene glycol and polyethylene glycol. The vitrifaction rapidly renders intracellular water into a vitrified state to avoid injuries or damages on cells caused by the formation of ice crystals. Nevertheless, it is very likely that the cells or the tissues are damaged by the high toxicity of the dense cryopreservation agents; thus, this technique is adopted in only some limited occasions.
In manufacturing pharmaceutical products, foods and ice sculptures for displaying purposes, additives such as sodium chloride or saccharides, glucose and trehalose, are used. Other additives such as antifreeze proteins or antifreeze glycoproteins are also used, which are made from organisms such as plants, fishes and insects (JP2005-126533A (Japan's patent application publication No. 2005-126533) and JP2003-250506A).
In a fuel cell, water is generated on either one of electrodes by an electrochemical reaction. For example, in a proton-exchange membrane fuel cell, water is generated on a cathode electrode; and portion of generated water runs to the anodal side through an electrolyte film. Water would also arise from the condensation of the vapor in a gas going into the cell. These types of water potentially obstruct the gas flow, deplete the supply of the gas itself and eventually decrease a battery performance. These complications can be prevented by treating the surface of a gas separator with hydrophilic coating materials such as proteins thereby limiting the water condensation, but the liquid water even in such a condition is occasionally frozen at low temperatures causing other complications. To circumvent this problem, polymer electrolytes with the antifreeze proteins are added to the resin layer, which is then to coat the surface of a polymer electrolyte film (Adler et al. listed in below), but this method has a problem of high cost.